Kaus Meridionalis, a bow star of Sagittarius

The Teapot is a familiar asterism of the southern sky. From the UK, it never climbs to a significant altitude when it’s at its highest point due south, so make sure you have a clear horizon in order to see it. It’s formed from a group of stars within Sagittarius, and the star Delta (δ) Sagittarii marks the point where the lid, body and spout are joined. It had the traditional name Kaus Meridionalis, which refers more to the mythological interpretation of Sagittarius as a centaur archer than a teapot!

There are three stars in Sagittarius named Kaus; Kaus Borealis (Lambda (λ) Sagittarii), Kaus Meridionalis and Kaus Australis (Epsilon (ε) Sagittarii). The name Kaus means ‘bow’, the ‘borealis’, ‘meridionalis’ and ‘australis’ means northern, middle and southern. In mythology the three stars represent the top, middle and bottom of Sagittarius’s bow.

The Bayer order in Sagittarius isn’t logical, with Kaus Australis brightest at mag. +1.8, then Nunki (Sigma (σ) Sagittarii) at mag. +2.0 and Ascella (Zeta (ζ) Sagittarii) at mag. +2.6. Kaus Meridonalis shines at mag. +2.7 and for once is well labelled as the delta star, because it’s the fourth brightest in Sagittarius. In case you’re wondering, Rukbat (Alpha (α) Sagittarii) is mag. +3.9, but it’s too far south to be seen from the UK.

Kaus Meridionalis is an orange-giant star with a spectral type of K3 III and an estimated distance from the Sun of 348 lightyears. It’s a binary system, the companion being a white dwarf. The primary is estimated to be 3.2 times more massive than the Sun with a diameter that’s 16 times larger. It is estimated to be 260 million years old.